FIG. 1 illustrates one type of electrically conductive workpiece, or preform 90, that is a closed bottom cylindrically shaped hollow metal preform with longitudinal axis L90. The closed bottom, as shown in cross section in FIG. 1, has a much greater thickness than the side wall of the preform. For example, for a preform with an overall cylindrical height of 4 inches and diameter of 0.2 inch, the side wall (90a) thickness may be on the order of 0.002-inch while the bottom and bottom side wall (90b) may be on the order of 0.1-inch.
A known method of heat treating such preforms is by passing a continuous row of preforms 90 through an electric induction tunnel furnace wherein a channel coil establishes a vertically oriented magnetic flux coupling with the preform structure to inductively heat the preform structure. Such heat treatment requires higher magnetic field intensities to heat the preform since the circumference of the preform is very highly conductive to a vertical field.
It is one object of the present invention to provide an apparatus and method for transverse flux electric induction heat treatment of electrically conductive articles or workpieces that have at least one section with a longitudinal axis, such as closed bottom cylindrically shaped hollow preforms, by establishing a flux field through the article that is either generally parallel to, or orthogonal to, the longitudinal axis of the section of the article depending upon the characteristics of the workpiece, to achieve a higher efficiency heating than presently known.
It is another object of the present invention to provide an apparatus and method for transverse flux electric induction heat treatment of electrically conductive articles or workpieces that are planarly-oriented, such as a blank for stamping into a coin, by establishing a flux field through the article that is generally orthogonal to the planar surface of the article.
It is another object of the present invention to provide an apparatus and method for transverse flux electric induction heat treatment of electrically conductive articles or workpieces that have two or more components with a longitudinal axis, such as a manifold, by establishing a flux field through the article that is either generally parallel to, or orthogonal to, the longitudinal axis of the two or more components of the article depending upon the characteristics of the workpiece, to achieve a higher efficiency heating than presently known.